View full sizeAssociated PressSan Francisco Giants' Melky Cabrera fouls off a pitch from Washington Nationals' Jordan Zimmermann in the fifth inning of a baseball game Tuesday in San Francisco.

SAN FRANCISCO -- San Francisco Giants outfielder Melky Cabrera has been suspended for 50 games without pay after testing positive for testosterone.

Cabrera was the most valuable player of the Staten Island Yankees in 2003.

The commissioner's office said Wednesday the suspension is effective immediately. Major League Baseball said Cabrera tested positive for the banned performance-enhancing substance, which violates MLB's joint drug prevention and treatment program.

"My positive test was the result of my use of a substance I should not have used," Cabrera said in a statement released by the players' union. "I accept my suspension under the Joint Drug Program and I will try to move on with my life. I am deeply sorry for my mistake and I apologize to my teammates, to the San Francisco Giants organization and to the fans for letting them down."

The MVP of the All-Star game last month in Kansas City, Cabrera is batting .346 with 11 home runs and 60 RBIs in his first season with San Francisco. He was initially in the lineup for the series finale against the Washington Nationals playing left field and batting third.

"We were extremely disappointed to learn of the suspension of Melky Cabrera for violating Major League Baseball's Joint Drug Prevention & Treatment Program," the Giants said shortly before game time. "We fully support Major League Baseball's policy and its efforts to eliminate performance enhancing drugs from our game. Per the protocol outline by Major League Baseball's collective bargaining agreement, the Giants will not comment further on this matter."

The 28-year-old Cabrera , who became a marketing phenomenon with nicknames like "Got Melk?", Melk Man and Melky Way, produced a 51-hit month in May. Cabrera batted .429 in May with three homers, five triples, seven doubles and 17 RBIs. He hit safely in 25 of 29 games. The 51 hits matched Randy Winn for most hits in a month since the club came to San Francisco in 1958.

Cabrera also set the San Francisco record for most hits in May, passing Hall of Famer Willie Mays' 49 from 1958.

Cabrera came to the Giants in a trade with Kansas City last November that sent left-hander Jonathan Sanchez to the Royals. Cabrera -- who signed a $6 million, one-year deal to avoid salary arbitration -- batted .305 with 44 doubles, 18 homers and 87 RBIs last season.